Glycoproteins (glycosylated proteins) are organic compounds composed of both a protein and a carbohydrate joined together by a covalent linkage. Glycosylated proteins are present on extracellular matrices and cellular surfaces of many cells. Oligosaccharides consist of a few covalently linked monosaccharide units, such as glucose and ribulose. The oligosaccharide moieties of glycoproteins are implicated in a wide range of cell-cell and cell-matrix recognition events.
The addition of carbohydrates such as oligosaccharides, on a protein involves a complex series of reactions that are catalyzed by membrane-bound glycosyltransferases and glycosidases. Glycosyltransferases are enzymes that transfer sugar groups to an acceptor, such as another sugar or a protein. Glycosidases are enzymes that remove sugar groups. The types and amounts of sugars that are attached to a given protein depend on the cell type in which the glycoprotein is expressed. In addition, the types of linkage used to join various sugar groups together also confound the complexity of glycosylation.
The biological activities of many glycoproteins are not detectably different if the carbohydrates are removed. However, glycosylation of proteins may have several effects. Carbohydrates often lengthen the biological life of a protein by decreasing the protein's rate of clearance from the blood. In addition, carbohydrates may help a protein to fold properly, stabilize a protein, or affect physical properties such as solubility or viscosity of a protein.
Phaseolamin is a glycoprotein found mainly in white and red kidney beans and is known to be an amylase inhibitor. Amylase is an enzyme responsible for the breakdown or digestion of starch. Starch is the main source of carbohydrates in the human diet. The digestion of starch begins in the mouth. Alpha-amylase present in saliva randomly hydrolyzes the α(1→4) glucosidic bonds of starch except for the outermost bonds and those next to branches.
By the time the thoroughly chewed food reaches the stomach, the average chain length of starch is reduced from several thousand to less than eight glucose units. The acid level in the stomach inactivates the alpha-amylase. Further digestion of starch continues in the small intestine by pancreatic alpha-amylase, which is similar to that of salivary alpha-amylase.
Decreasing the absorption of carbohydrates by inhibiting the digestion of starch is a very promising strategy in the fields of, for example weight loss and diabetes mellitus. From a dietary standpoint, it is important to target the breakdown of starch since starch is a relatively nonessential nutrient, which provides calories with fairly little benefit. Furthermore, as starch is broken down into simple sugars and absorbed from the digestive tract, the pancreas is triggered to produce insulin. Increase in insulin production causes an individual to feel hunger.
Several clinical studies, however, demonstrated that commercially available crude bean amylase inhibitors, when given with a starch meal, failed to influence fecal calorie excretion, postprandial concentrations of plasma glucose or breath hydrogen, and metabolism of 13C-labeled starch. In addition, administration of amylase inhibitors has been associated with side effects, such as abdominal discomfort and diarrhea.
It is estimated that approximately 40% of the United States population suffer from obesity (Glazer, G. (2001) Arch. Intern. Med. 161: 1814–1824). Obesity has been associated with many illnesses, such as cardiovascular disease, respiratory illness including asthma, sleep apnea, pick-wichian syndrome, diabetes mellitus and pulmonary hypertension. In addition, adenocarcinoma of the esophagus and gastric cardia (Lagergren, J. et al. (1999) Ann. Intern. Med. 130: 883–890), hepatic necrosis, and cirrhosis (Ratziu, V. et al. (2000) Gastroenterology 118: 1117–1123) have recently shown strong correlation with obesity.
Approximately 90% of all obese individuals who try to lose weight fail. One reason is that the majority of obese individuals are reluctant to give up eating certain foods, including starches (i.e., pasta, bread, and potatoes). Therefore, a dietary supplement that effectively inhibits the digestion and breakdown of starch, without harmful side effects, will be beneficial in helping these individuals achieve weight loss.
In addition to assisting weight loss, inhibiting the digestion or breakdown of starch may also be beneficial in illnesses such as, for example, diabetes mellitus. Currently, between 120 and 140 million people worldwide suffer from diabetes mellitus and by the year 2025, it is estimated that this number may double. Much of the increase in individuals suffering from diabetes mellitus will occur in developing countries due to population aging, unhealthy diets, obesity, and a sedentary lifestyle.
Diabetes mellitus is a chronic disease characterized by a deficiency in the production of insulin by the pancreas, or by ineffectiveness of the insulin produced to utilize glucose. This impairment in glucose utilization results in increased concentrations of glucose in the blood, which leads to damage of many of the body's systems, such as the blood vessels and nerves. Therefore, preventing the breakdown of starch into smaller sugar units, such as glucose, will be beneficial in the prevention and/or treatment of diabetes mellitus.
Numerous articles have been published concerning amylase inhibition. Some of these articles have indicated that amylase-inhibitors worked well in vitro, but failed to be effective in humans. Some of the proffered reasons were 1) insufficient activity; 2) destruction in the gastrointestinal tract; 3) suboptimal pH conditions; and 4) differing gastric emptying rates of starch and inhibitor.
Previous attempts to block starch absorption have failed for many reasons including the instability of the starch-blockers employed. Thus, there remains a need for a stable, inhibitor of starch digestion with enhanced bioactivity and decreased side effects.